if anyone is still looking for an idea their kids can make for gifts we did these yesterday and they came out awesome. super easy, fairly cheap (the balls are 50% off at michael's this week) and we were able to crank out 12 in about an hour. http://pinterest.com/pin/165296248792941333/
at first I giggled at the name (because I'm 12), but once I looked at them I had to bookmark. I'm goin to try and snag some as well after Christmas on sale and make them as gifts next year. Very neat.
Similiarly, my coworker recommends swishing the inside of a clear bulb with rubbing alcohol. Then, take two different colored paints and slowly swirl them inside the bulb. The alcohol keeps them from mixing. Drain the excess and allow to try. They look really cute too.